The invention relates to a magnetic multilayer device comprising two layers of magnetic material which are separated by an interposed layered structure.
The invention further relates to the application of such a device in a magnetic recording head.
Multilayer devices as described in the opening paragraph are well known in the art, and are elucidated inter alia in the article by Parkin et al. in Phys. Rev. Lett. 64 (1990), pp 2304-2307, which is devoted to Co/Ru, Co/Cr and Fe/Cr superlattices. Multilayers such as these comprise alternately stacked layers of ferromagnetic material (Co or Fe) and non-magnetic material (Ru or Cr), and are particularly suitable for application in magneto-resistive field sensors, such as magnetic read heads. The so-called spin-valve magneto-resistance effect on which such sensors are based relies on the fact that the measured electrical resistance of the multilayer structure is determined by the mutual magnetisation configuration in the ferromagnetic layers, said resistance being (generally) higher for an anti-parallel configuration than for a parallel configuration. In the known structures, this configuration can only be controllably adjusted by suitable application of an external magnetic field, as elucidated for example in U.S. Pat. No. 5,134,533.
The above-cited article particularly describes how the exchange-coupling between consecutive ferromagnetic layers in the known structures is dependent on the thickness of the interposed non-magnetic layers. For example, it is revealed that such coupling can be either ferromagnetic (F) or antiferromagnetic (AF), depending on the exact interlayer thickness. This is an interesting phenomenon, since F coupling will produce a mutually parallel magnetisation configuration in consecutive ferromagnetic layers, whereas AF coupling will cause a mutually anti-parallel magnetisation configuration. These different magnetisation configurations will in turn correspond to substantially different magnetic flux distributions for the sample. Unfortunately, however, interlayer thickness is not a parameter which can be varied subsequent to the multilayer structure's manufacture, so that such controllable adjustments of the exchange coupling are not practically attainable in a finished structure of the known type.